Fix ul > li > p styling
Fix ul > li > p styling

This was broken in /speaking/talk/ (this page isn't present in the
menu, and was overlooked). display: table-cell makes multiple
paragraphs span out *horizontally*, so we need to clear: both to
make them break as they should.

pycontw/pycontw2016,pycontw/pycontw2016,pycontw/pycontw2016,pycontw/pycontw2016